A schematic does not have to be well-drawn to become net-listed and turned into a PCB layout, but turning a PCB layout back into a functionally informative schematic takes more effort.
Why a single page? Herein lies a TinyCAD weakness -- highlighting a net (more on this later) will crossover between sheets when all of the sheets are in the same drawing set, but only one sheet of this set can be made visible at any particular time. Bummer. This makes it hard to see all nodes of a net on-screen at a glance. To view more than one sheet at a time, one can open a second iteration of TinyCAD to show another sheet, but -- in this case -- highlighting a net will not crossover between sheets. Making component graphics small enough to get the whole PCB on a single sheet makes net highlighting visible across the whole page.
The result is a horrendously complex and un-readable schematic when printed onto paper. But this is NOT the schematic that will be viewed by anyone other than the reverse engineer. Its only purpose is to transform a physical PCB layout into an on-screen drawing that captures the physical layout. The functionality schematics come later after the physical schematic nets have been deciphered and re-drawn to show meaningful functionally.
The grid can be set to whatever size the user wants, but I have found that too small a grid can cause problems with block copies and moves. Best leave the grid size at "fine," and instead increase your drawing area by enlarging the page size as needed. For example, selecting a European page size A2 with font size 6 and printing at 64% scale on 11" x 17" paper gives you a single page drawing that is still readable, if you are getting on in years, a magnifying head visor helps. Printing the same at 129% gives you four 11" x 17" pages that can be taped together to give you a readable print copy. But most reading will be done on-screen, and the zoom and pan functions are very easy using the mouse scroll wheel and right-click-drag, respectively.
Another tip to work around a TinyCAD weakness is to keep "Junction Dot Placement" set to automatic. While an option for manual placement can be used, block moves afterwards cause wires to "bend" and you will have to go in and straighten them all out again.
Reverse analysis is a two-pass effort requiring an initial physical schematic based on actual PCB placement and package pinouts. This is followed by a series of functional schematics that re-draw the captured circuits in a logical and comprehensible fashion (and also catch errors when the functions appear to make no electrical sense). The physical schematic is a representation of the PCB as viewed from above.
Components are drawn in the same orientation as on the PCB; transistors are shown in their representative packages with GDS or EBC physical pins; relay switches are sown with their terminals arranged in the same way as they appear from the top; ICs are drawn in their packages with their internal logic elements or functional names shown. Many times, a PCB does not have reference designators in the silkscreen, so relating a component location to a later functional schematic depends very strongly on the physical schematic.
A physical representation can look like the image shown below. Orange is topside, green is bottomside surface mount components. Some capacitor graphics look shorted because a TinyCAD bug does not always transfer the invisible masking square when copying and pasting a selected block portion to MS Word. It would be nice if TinyCAD had a "group" function to tie graphic elements together, but one must resort to drawing a box around the graphics each time they need to be moved or copied.
Confusing, yes? It's impossible to figure out what is going on electrically from the above image. However, once this has been re-drawn into a meaningful functional schematic, the result is a very readable and understandable depiction as illustrated below:
This image is under construction. Temporarily color-coding the nets on the physical drawing make transfer to the functional drawing less prone to error. Elastic wires follow components when dragged around for readability. Unfortunately, TinyCAD does not keep wires connected when a component is rotated or flipped (mirror imaged).
When drawing the bottom-side physical component locations, it can help to first draw the area partially to scale as seen from the bottom-side, then draw a block around the circuit and flip horizontally (mirror image) to make it a topside view as seen through the PCB, and then add the topside components. Obviously there has to be some adjustment in relative positions that do not allow exact scale representation, and the connecting wires have to fit too.
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